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authorHidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>2009-11-26 00:49:27 -0500
committerIngo Molnar <mingo@elte.hu>2009-11-26 06:59:20 -0500
commitb7b20df91d43d5e59578b8fc16e895c0c8cbd9b5 (patch)
tree9ad1a2347264db548a161575080ed3bdc32f6d51 /kernel/time.c
parentd5b7c78e975302a1bab28263266c39ecb71acad4 (diff)
sched, time: Define nsecs_to_jiffies()
Use of msecs_to_jiffies() for nsecs_to_cputime() have some problems: - The type of msecs_to_jiffies()'s argument is unsigned int, so it cannot convert msecs greater than UINT_MAX = about 49.7 days. - msecs_to_jiffies() returns MAX_JIFFY_OFFSET if MSB of argument is set, assuming that input was negative value. So it cannot convert msecs greater than INT_MAX = about 24.8 days too. This patch defines a new function nsecs_to_jiffies() that can deal greater values, and that can deal all incoming values as unsigned. Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Spencer Candland <spencer@bluehost.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Amrico Wang <xiyou.wangcong@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: John Stultz <johnstul@linux.vnet.ibm.com> LKML-Reference: <4B0E16E7.5070307@jp.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/time.c')
-rw-r--r--kernel/time.c30
1 files changed, 30 insertions, 0 deletions
diff --git a/kernel/time.c b/kernel/time.c
index 2e2e469a7fec..804798005d19 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -662,6 +662,36 @@ u64 nsec_to_clock_t(u64 x)
662#endif 662#endif
663} 663}
664 664
665/**
666 * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
667 *
668 * @n: nsecs in u64
669 *
670 * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
671 * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
672 * for scheduler, not for use in device drivers to calculate timeout value.
673 *
674 * note:
675 * NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
676 * ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
677 */
678unsigned long nsecs_to_jiffies(u64 n)
679{
680#if (NSEC_PER_SEC % HZ) == 0
681 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
682 return div_u64(n, NSEC_PER_SEC / HZ);
683#elif (HZ % 512) == 0
684 /* overflow after 292 years if HZ = 1024 */
685 return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
686#else
687 /*
688 * Generic case - optimized for cases where HZ is a multiple of 3.
689 * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
690 */
691 return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
692#endif
693}
694
665#if (BITS_PER_LONG < 64) 695#if (BITS_PER_LONG < 64)
666u64 get_jiffies_64(void) 696u64 get_jiffies_64(void)
667{ 697{